This invention relates generally to a method for manufacturing golf balls and specifically to a method for forming non-circular dimples in the surface of the ball.
Golf balls are now being produced having various dimple patterns, dimple sizes, and geometric dimple patterns. Generally speaking, all of these dimples are configured so as to have a substantially constant geometric surface. Whether circular or multi-sided, the dimples are designed so that the geometrical configuration of each dimple is substantially the same regardless of its size. In this type of dimple arrangement, the dimples are normally configured in some pattern such as an octahedron, dodecahedron, or the like, or are configured so as to provide sections within each hemisphere in the ball surface, whether those sections number four, or six, or whatever desired configuration. Normally, the dimples are arranged in a desired pattern within each section and then this pattern is repeated for each section. The standard procedure is that each hemisphere has the same number of dimples and in substantially the same pattern and the hemispheres may be rotated with respect to each other depending upon the position of the mold halves.
The mold halves have dimple patterns formed therein so that when the cover layer is formed on the ball, the outer surface of the cover will be indented with the desired dimple pattern and configuration. The most common dimple configuration is a circular dimple.
It is well-known in the patented prior art to form a hob having approximately the same dimensions as half of the finished golf ball and then forming a mold from the hob as disclosed in the Brown et al U.S. Pat. No. 3,831,423. The hob is drilled to a desired depth to define the circular dimples to be formed in the golf ball surface. Thus, the resulting mold has the desired dimple depth and configuration formed therein.
It is also known in the art to machine a mold for a golf ball using an electric discharge machine (EDM) electrode as disclosed in the U.S. patent to Underwood et al U.S. Pat. No. 4,954,022. A numerically controlled cutting tool is used to drill holes in the electrode to a uniform depth. During electrode discharge machining of the mold, bumps are formed in the mold surface by the holes in the electrode. The bumps define the dimples in the golf ball surface.
EDM technology has also been used to form a master die used to mold non-circular dimples in the surface of a golf ball as shown by the Banji U.S. Pat. No. 5,406,043.
While the prior methods and devices for machining molds for golf balls normally operate satisfactorily, they possess certain drawbacks. One such drawback is the expense required for EDM devices and numeric controls therefor. Another drawback is that the EDM technology is not as precise as prior drilling techniques. Thus, the molds formed thereby do not define clear accurate dimples, particularly where the dimples are non-circular.
The present invention was developed in order to overcome these and other drawbacks of the prior devices by providing an improved machining process for forming a hob used to create a mold for forming golf balls with non-circular dimples.
Accordingly, it is a primary object of the present invention to provide an improved method for forming non-circular dimples on a spherical surface using a pantograph for consistency in the configuration of all of the dimples. A first portion of the surface is drilled along a radius thereof to a first depth with a drill bit. Next, the drill bit is displaced relative to the surface along a given path defined by a pantograph without altering the axial orientation of the drill bit in order to form a non-circular dimple in the surface. The drill bit is then withdrawn from the surface and the surface is rotated to arrange a second portion of the surface beneath the drill bit. The drilling, displacing and withdrawing steps are repeated to form subsequent dimples in the surface, with all of the dimples having the identical non-circular configuration.
According to a further object of the invention, the drill bit is maintained at the first depth during the displacement steps so that an edge of each dimple is defined where the drill bit leaves the spherical surface.
Alternatively, the drill bit may be axially displaced relative to the first depth during the displacement steps so that the dimples have a variable depth.